This invention relates to a head actuator for a disc drive and storage system used for supporting a plurality of read/write heads over the surfaces of a plurality of discs. More particularly, this invention relates to a head actuator for a Winchester type of hard disc drive and storage system.
In recent years, there has been a demand for higher storage capacity in disc drive and storage systems. Two methods of achieving a higher capacity are: (1) improving the recording density of the disc and (2) increasing the number of discs. When the number of discs are increased, the number of read/write heads also increase in relationship to the number of discs. Such heads are normally provided in an assembly comprising head arms and load springs corresponding to the heads being used (hereafter referred to as a "head actuator"). Such head arm/spring assemblies are conventionally made by stacking or positioning in parallel series the head arms of the same shape as will be described below by reference to prior art FIGS. 1 and 2.
FIG. 1 is a schematic cross-sectional view of a primary part of a conventional disc drive and storage system. FIG. 2 is a schematic cross-sectional view of a primary part of a head actuator for the prior art disc drive and storage system shown in FIG. 1. As shown in these figures, a base 1 is provided having a spindle 2 thereon for rotatably mounting a plurality of magnetic storage discs 3. A spindle motor (not shown) is normally located inside of the spindle 2 for rotatably driving the spindle. The plurality of magnetic storage discs 3 are located on the spindle 2 and are spaced apart from one another in parallel series. The discs 3 are rotated at a constant high speed (for example, 3600 rpm) by the driving force of the spindle motor. A head actuator 4 is located adjacent the discs 3 to move data write/read heads 5 to target tracks on the discs 3. The plurality of heads 5 are attached to respective outer ends of load springs 6 through zimbal springs. The other inner ends of the load springs 6 are connected to respective outer ends of a plurality of corresponding head arms 8 using a series of screws 7. The head arms 8 are aligned in parallel series and stacked through a plurality of separate spacers 9 and are integrated or assembled together using a screw 10 and a nut 11. As shown, the heads 5, the load springs 6, the head arms 8 and the spacers 9 are formed in the same shape for the respective components. The assembled head arms 8 are provided with a fixed driving coil 12. A yoke 13 is provided on the base 1 and comprises an inner yoke 13a and an outer yoke 13b. Magnets 14 are located on the internal wall surfaces of outer yoke 13b and are magnetized in the vertical direction as seen in FIG. 1. The driving coil 12 is located in the magnetic gap between the magnets 14 and inner yoke 13a.
In this type of head actuator structure, each of the head arms 8 are separately formed in the same shape and each of the spacers 9 are separately formed in the same shape. Accordingly, large numbers of each components are generally produced in unit lots during manufacturing. Thus, for a particular lot, the shape and size of a component can often deviate in a single dimension from the pre-determined dimension allowance. For example, FIG. 3 depicts the primary part of the head actuator of the FIG. 1 prior art, and what the positioning of the head arms could be to the discs after assembly when the thickness dimension of the head arms 8 deviates and exceeds the pre-determined tolerance allowance. FIG. 4 depicts the primary part of the head actuator of the FIG. 1 prior art, and what the positioning of the head arms could be to the discs after assembly when the spacers 9 have one of the end surfaces inclined out of the normal tolerance allowance. In FIG. 3, the pitch between head arms 8 becomes larger than that between the discs 3. Therefore, an adverse effect can be created on the flying characteristics and data write/read characteristics of heads 5. In FIG. 4, the heads 5 are no longer parallel to the discs 3. Again, an adverse effect can be created on the head flying characteristics.
With a demand to improve storage capacity, the number of discs increases and the out-of-tolerance conditions can become further magnified under conditions as described above. When dimension tolerances are tightened to solve these problems, manufacturing costs increase. Moreover, the additional stacking of a plurality of the head arms 8 creates increased assembling labor time and costs because more heads 5 have to be accurately located at the pre-determined outer radius surface positions on the discs 3. Also, problems arise where an axial or tightening force of the screw 10 is weakened due to temperature changes in the disc drive and storage system, deviation in stacking or alignment of the head arms 8 is generated, and thereby data write/read operations become more difficult.
Recently, there has been developed a type of head actuator for a disc drive and storage system which has integral head arms in an effort to solve some of the above problems. Examples are shown in U.S. Pat. No. 4,796,122, U.S. Pat. No. 4,829,395 and Japanese Unexamined Patent Publication (Kokai) No. 63-188878. This type of head actuator has an integral head arm body with a plurality of integral head arms. The integral head arms extend outwardly from the body to support load springs. The load springs are assembled after the integral arms and arm body are formed.
In the above type of integral head actuator, the load springs must again be connected to the outer ends of the integral head arms. The load spring connecting technique requires a special tool, or a special material, such as a connecting block, and several screws for connecting the load springs to this type of integral head arm body. For example, in this type of head actuator using a connecting block, an intermediate material is located between the head arms and the load springs with connection then by several screws. The purpose of using the intermediate material is to change the force direction of the screws from a perpendicular direction to a direction parallel to the axis of the head arms. In this connecting technique, the load springs for the upper and lower sides of a disc are first connected to the intermediate material by screws from a perpendicular direction compared to the axis of the head arms. Then, each intermediate material fitted with the load spring must be connected to the outer end of each head arm by screws from a direction parallel to the axis of the head arms.
In the alternative embodiment of this type of head actuator, the load springs are directly connected to the head arms by screws at the outer ends of the head arms. However, in this embodiment standard type load springs, such as a flat type load spring shown in U.S. Pat. No. 4,796,122, cannot be used. The end portion of the load spring must be customized to an L-shape bracket for connecting it to the head arms by screws at the outer end of the head arm.